Pyrogen and canister incorporating pyrogen

ABSTRACT

The pyrogen of the invention is formed by the compression of ferrosilicon powder and a mixture of ferric oxide powder and another lower order iron oxide powder. This pyrogen overcomes the weaknesses inherent in earlier pyrogens by dispensing with the use of peroxides. The scope of the invention also extends to the canister which holds the pyrogen. The pyrogen, which is positioned inside the canister&#39;s combustion chamber in such a way that it comes into contact with the top of said combustion chamber, is supported by a special ceramic thermal insulator which contains an ignition device comprising an ignition agent, which also incorporates an instant high temperature generating ignition material, and a match head chemical which projects out of a hole in the base cover of the canister. The bottom of the canister is covered by a bottom cap which can be freely removed or replaced as required. The canister, which enables the heating or cooking of whatever is placed inside it, is compact, safe and cheap.

This is a divisional application of Ser. No. 07/789,589, filed Nov. 8,1991 now abandoned.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention relates to a pyrogen, which depends for its heating effecton a metal redox reaction, and a self-heating canister whichincorporates said pyrogen and which is used either to cook or simply toheat up various foodstuffs such as grains, noodles and beverages.

2. Description of the Prior Art

A substantial number of proposals have already been made in respect ofpyrogens which make use of the exothermic oxidation of metals (forexample: Japanese patent publication gazette S27-582, Japanese utilitymodel laying open gazette S58-24119, and Japanese patent laying opengazette S62-17287, S63-51491, and H1-284582). All these proposals haveinvolved the admixture of metal oxides and peroxides to one or more ofthe powders of iron, aluminum and ferrosilicon.

When a pyrogen which makes use of peroxides in this way burns, however,the peroxides not only react with the Si but also break down through aprocess of pyrolysis. This results in the freeing of oxygen gas which inturn facilitate the generation of sparks and flames which are sometimesemitted from the container thereby creating an obvious hazard. Anotherdrawback with this type of pyrogen derives from a tendency to swellrapidly following combustion and to assume a sort of sponge like formunder the influence of the aforementioned free oxygen gas. Japanesepatent laying open gazette H1-288218, on the other hand, disclosed theuse of a pyrogen composed of ferrosilicon powder plus one or both of thesubstances Fe₂ O₃ and CuO. Since the pyrogen does not in this casecontain peroxides, the amount of oxygen gas which is freed isconsiderably reduced but even so, since it is not, in fact, altogethereliminated, the aforementioned problem of the swelling and deformationof the pyrogen following combustion remains.

SUMMARY OF THE INVENTION

Un order to solve the problems outlined above, the inventors conducted anumber of tests and studies as a result of which they perfected thepyrogen of the invention which is characterized by the fact that it isan oxide which has the potential to remain stable at high temperatureswhile at the same time giving up oxygen to the Si.

The pyrogen of the invention is formed by the compression of a metalpowder and a metal oxide powder where said metal powder consists ofpowdered ferrosilicon and said oxide powder consists of a mixture ofpowdered ferric oxide (Fe₂ O₃) and another powdered iron oxide of alower order (Fe₂ O₃ -x where x=0.2 to 1.0). In this pyrogen said mixtureof ferric oxide powder with a powdered iron oxide of a lower orderperforms the role of oxygen donor, thereby dispensing with the need fora peroxide to act as said donor. During combustion, therefore, thepyrogen does not produce free oxygen, with the result that the pyrogenitself does not swell and the combustion process is able to proceed at asmooth and easy pace without the generation of sparks or flames. Theinvention can thus be used either to cook or simply to heat up variousfoodstuffs, thereby making it a perfect portable heat source.

A self-combusting pyrogen which derives its heat from the exothermicoxidation of powdered metal offers the advantage of generating a higherlevel of heat during the course of a reaction than is produced by themore conventional lime based pyrogens which make use of the heat whichis generated by the addition of water to quick lime. For this reason, ithas proved possible to generate sufficient heat with the pyrogen of theinvention to produce boiling, a function which has not hitherto beenachievable using lime based pyrogens. This in turn raised thepossibility of creating some sort of canister in which to incorporatesuch a boiling function based on the utilization of this type ofself-combusting pyrogen.

However, if this type of canister is to be produced on a commercialbasis then the complexity of the thermal insulation structure requiredwould be likely to necessitate the use of a fairly large canister whilethe sort of ignition device required to generate the high ignitiontemperature needed by the heating agent would almost certainly force upthe container's production costs and taken together these drawbackswould impair its practical value as a disposable canister.

In order to solve the problems outlined above, the inventors conducted anumber of tests and studies as a result of which they successfullydeveloped the canister of the invention which is characterized by thecompactness and high heat generation of the pyrogen and its accompanyingthermal insulator and the rational structure of the related ignitiondevice.

The object of the invention is to provide a cheap, safe canister whichcalls simply for the adjustment of the amount of pyrogen to enable it tobe used to heat a variety of different foodstuffs ranging from thosewhich are sometimes referred to as "fever foods" (hereafter referred tosimply as "FF") and which require boiling or proper cooking such asgrains like rice, cereals and beans or noodles such as udon, soba orinstant ramen through to those which are sometimes referred to as "feverdrinks" (hereafter referred to simply as "FD") and which only requirewarming up at a single predetermined temperature such as sake, coffee,tea and other similar drinks and prepared foods such as western typesoups, miso soup and rice porridge.

In order to achieve this object, the canister of the invention has beendesigned such that the lower part of the canister incorporates acombustion chamber which in turn houses a pyrogen which comes intodirect contact with the top of said combustion chamber and which isformed by the compression of ferrosilicon powder and a suitable mixtureof ferric oxide powder and a powdered iron oxide of a lower order. Thepyrogen itself is in turn supported by a special ceramic thermalinsulator with a hole through the middle. The hole in the middle of thethermal insulator is packed with an ignition device which comprises twodistinct layers of material, the upper layer consisting of an instanthigh temperature generating ignition material and the lower layerconsisting of an ignition agent, along with a match head chemical whichprotrudes from the bottom of said ignition device out through a hole inthe base cover of the canister. The bottom of the canister itself isfitted with a cap which is designed such that it can easily be removedor replaced as necessary. The use of a solid pyrogen in combination witha thermal insulator made of a special highly heat resistant ceramic havetogether facilitated the creation of a more compact, lighter weightcanister and this has in turn enabled a reduction of approximately 60%in the cubic capacity of the combustion chamber compared with that of amore conventional canister. As a result it is now possible to heat agiven volume of material to a given temperature using an aluminumcanister which is approximately 25% lighter in weight than the sort ofconventional canister which would have been necessary to heat anidentical volume of material to an identical temperature.

Moreover, whether it is used for FF or for FD purposes. The canister ofthe invention accepts part of the food contents into the space betweenthe outer wall of the combustion chamber and the inner wall of the mainbody of the canister itself, at least for the upper part of thecombustion chamber, and this serves to increase the overall adiabaticeffect in this part of the canister. Particularly in cases where thecanister is structured such that the pyrogen is supported by projectionson the upper surface of the thermal insulator, an air-filled layer iscreated in the space between the pyrogen and the insulator and thisfurther enhances the adiabatic effect while at the same time increasingthe safety of the canister's design.

The pyrogen used in the canister of the invention has a high combustiontemperature (normally about 1,400° C.) and is, therefore, fully capableof supporting the sorts of temperatures required for the boiling orwarming of foodstuffs and it has been possible, as a result, to achievevery substantial reductions by comparison with conventional canisters inthe length of time required from the point of ignition through to thepoint at which the food or drink in the canister is ready forconsumption. Furthermore, since the aforementioned pyrogen does notchange into a powdered form following combustion and since it alsoexhibits only minimal cubical expansion, disposal after use is easy. Thethermal insulator referred to above is itself a specially manufacturedcompact, light weight ceramic with outstanding heat resistingcharacteristics. This enables substantial reductions in the level ofexternal heat emission from the canister while at the same timefacilitating the achievement of more thermally efficient boiling andheating operations. In the case of canisters used for the heating of FD,there is a space of constant size between the wall of the combustionchamber and the inner wall of the canister and this creates an overheatprotection effect. Also, in the case of canisters used for the heatingof FF, which are constructed in such a way that the lower part of thethermal insulation comes directly into contact with the inner wall ofthe canister, a similar overheat protection effect is neverthelessafforded by the fact that the inner wall of the canister in the vicinityof the upper half of said thermal insulation from which a significantamount of heat is emitted, is normally in contact with some sort ofliquid or steam. There is, moreover, a layer of air sandwiched betweenthe bottom cap and the base cover of the canister which serves toeliminate the risk of overheating or burning of articles close to thecanister as a result of an abnormal temperature rise in the body of thecanister itself, even when using a pyrogen with an extremely highcombustion temperature.

The ignition device consists of a combustion of a low temperatureignition agent and an instant high temperature generating ignitionmaterial. It is thus possible to ignite the pyrogen quickly and easilyusing a match head chemical while at the same time keeping to a minimumthe amount of canister space required to house the ignition deviceitself. The canister is also fitted with its own water pack in caseswhere it is to be used for the purpose of boiling FF type foods such asrice. Moreover, since the pack itself is made of a quick meltingmaterial, even if the user forgets to empty the contents of the waterpack over the rice but still ignites the canister, once the water startsto boil the high temperature inside the water pack will quickly melt thepack material, thereby releasing the water and preventing the canisterfrom boiling dry.

Since the component parts such as the pyrogen, the thermal insulationmaterial and the ignition device, which make up the interior of thecombustion chamber, have been made more compact than those used in moreconventional canisters, it is not possible to use a smaller canisterthan would previously have been required to heat up any given amount offood or drink. Since the component parts themselves are also cheap, theproduction cost per canister is low and this makes the final productwell suited to use as a self-heating, throw-away canister.

The use of a powerful fireproof adhesive to cement the connectionsbetween the canister parts and the pyrogen and thermal insulationmaterials, for example, also helps keep the cost of production downwhile at the same time increasing the design safety of the finishedproduct by making it more difficult to disassemble.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a longitudinal sectional view illustrating the basic form of acanister containing a pyrogen.

FIG. 2 is a longitudinal sectional view of the central part of acanister designed for use with FF.

FIG. 3 is a longitudinal sectional view of the central part of acanister designed for use with FD.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Basically any pyrogen made by compressing ferrosilicon powder and asuitable mixture of ferric oxide powder (Fe₂ O₃) and a powdered lowerorder oxide of iron (Fe₂ O₃ -x where x=0.2 to 1.0) would constitute avalid example of the preferred embodiment. However, if a reallyexcellent level of performance is to be obtained, then the metalconstituents must each conform to their respective specifications asdetailed below.

First, the amount of ferrosilicon powder added to the mixture shouldideally be between 20 and 35 parts by weight. The reason for this isthat anything less than 20 parts increases the tendency of the mixtureto burn erratically, thereby impairing the smoothness of the combustionprocess. The addition of more than 35 parts of ferrosilicon, on theother hand, tends to reduce the amount of heat generated per unit ofweight. The ideal average diametric size of the particles offerrosilicon powder is 20 microns. The reason for this is that anaverage particle size of more than 20 microns tends to make the finalmixture more difficult to ignite, thereby impairing the overallsmoothness of the combustion process. The Si content of the ferrosiliconitself should be at least 75%.

The amount of ferric oxide added to the mixture should ideally bebetween 10 and 50 parts by weight. The reason for this is that theaddition of less than 10 parts by weight may result in an excessivereduction in the strength of the pyrogen after compression while theaddition of more than 50 parts may result in an excessive reduction inthe effect obtained through the addition of iron oxides of a lower order(Fe₂ O₃ -x). The ideal average diametric particle size of the ferricoxide powder is 10 microns or less. Impurities in the ferric oxide suchas S, Cl and SO₃ should also ideally be kept to a minimum.

The lower order iron oxide Fe₂ O₃ -x powder referred to above can easilybe obtained by the partial reduction of ferric oxide (Fe₂ O₃). It isalso possible to use substances obtained through the neutralizationoxidation of bivalent Fe, for example, or else a fine particulate of anaturally occurring low order oxide iron ore. Magnetite, which is atriiron tetroxide (Fe₃ O₄) in which the x value of Fe₂ O₃ -x isapproximately 0.33, is particularly suitable for use as the principallower order iron oxide since it is both cheap and easy to obtain.Triiron tetroxide also has a number of other outstanding features inthat it is, for example, even more stable than ferric oxide at hightemperatures, it does not easily give up oxygen even in response to theheat of combustion of Si, it tends to absorb free oxygen released by theferric oxide and it is thus conducive to the suppression of problemssuch as cracking or expansion of the pyrogen following combustion.Moreover, by using triiron tetroxide in combination with an Fe₂ O₃ -x inwhich the x value is between 0.2 and 1.0, the combustion process isrendered more gentle than the produced by a pyrogen which uses onlyferric oxide to contribute oxygen to the Si. It is possible, therefore,in this sort of case to adjust the speed of the combustion processitself. The amount of said lower order iron oxide powder Fe₂ O₃ -x addedto the mixture should ideally be between 20 and 60 parts by weight. Thereason for this is that the addition of less than 20 parts by weightwould tend to lead to a reduction in the effect obtained by adding alower order iron oxide (Fe₂ O_(3-x)) to the mixture while the additionof more than 60 parts by weight, on the other hand, would tend to reducethe amount of heat generated per unit of weight while at the same timeleading to a reduction in the strength of the mixture after forming. Theideal average diametric size of the particles of the lower order ironoxide Fe₂ O₃ -x is 10 microns or less. The powdered lower order ironoxide Fe₂ O₃ -x should preferably contain only minimal amounts of thetypes of impurities which are likely to become gaseous at hightemperatures. Although it would be possible to facilitate the adjustmentof the speed of combustion of the Si and Fe₂ O₃ by incorporating intothe pyrogen a substances such as alumina, silica or powdered rock whichwould not act as oxygen donors, the problem is that even the addition ofonly very small amounts of such substances tends to result in theimpairment of smooth combustion and may even result in prematuretermination of the combustion process. The addition of such substancesshould, therefore, be avoided wherever possible.

The aforementioned pyrogen can be compressed into a variety of shapessuch as pillar or plate shapes as required. Powdered ferrosiliconcombined with a suitable mixture of powdered ferric oxide and a lowerorder iron oxide powder could also, for example, be compressed withoutfurther preparation in a metal mold to between 200 and 500 kg/cm². Asimilar mixture could, on the other hand, be compressed to just 100 to300 kg/cm² after the addition of between 1.0% and 3.0% of some sort ofnon-combustible ceramic based binder.

Preferred embodiments No. 1 to No. 12 of the pyrogen will now bedescribed in some detail.

Preferred Embodiment No. 1

30 parts by weight of a ferrosilicon (Fe: 25%, Si: 75%) particulate withan average diametric particle size of 8 microns, 30 parts by weight ofan Fe₂ O₃ particulate with an average diametric particle size of 2microns and 40 parts by weight of a magnetite (mainly Fe₃ O₄, x=0.33)particulate were mixed together to form 15 g of powder which was thenplaced inside a metal mold with a diameter of 3 cm and compressed at 300kg/cm² to form a pyrogen of 1.0 cm in thickness.

The pyrogen 2 was first placed on top of the thermal insulator 3 shownin FIG. 1. Approximately 0.2 g to 0.3 g of a mixture of iron,ferrosilicon, copper oxide and barium peroxide powders was then placedmore or less in the center of said pyrogen 2 to act as an ignition agent4. 180 ml of water 5 at a temperature of 20° C. was then powered intothe aluminum canister 1 shown in FIG. 1 and then, after igniting theaforementioned ignition agent with a match, the pyrogen 2 wasimmediately inserted into the recession in the base of the aluminumcanister 1 along with the thermal insulator 3. At the end of 5 minutesthe temperature of the water was measured and was found to have risen to51° C. It was also found that the pyrogen 2 continued to burn gentlyafter it was inserted into the bottom of the aluminum canister 1 andthat the diametric expansion of the pyrogen 2 after combustion was notmore than 1.0 mm.

Preferred Embodiments No. 2 and No. 3

Apart from altering the Fe₂ O₃ and the Fe₃ O₄ mixture ratios, the risein the temperature of the water was in each case measured under exactlythe same conditions as those described in connection with preferredembodiment No. 1 above. The results of the measurements taken are shownin Table 1 below. The combustion of the pyrogens proceeded smoothly ineach case while the expansion of the pyrogens following combustion wasagain no more than 1.0 mm in either case.

                  TABLE 1                                                         ______________________________________                                        Preferred              Water temperature                                                                         Absolute rise in                           embodi-                                                                              Fe.sub.2 O.sub.3                                                                      Fe.sub.3 O.sub.4                                                                      after 5 minutes                                                                           temperature                                ment No.                                                                             (%)     (%)     (°C.)                                                                              (°C.)                               ______________________________________                                        No. 2  10      60      49          29                                         No. 3  50      20      53          33                                         ______________________________________                                    

Preferred Embodiments No. 4 to No. 7

Apart from altering the Fe₂ O₃ and the Fe₃ O₄ mixture ratios, the risein the temperature of the water was in each case measured under exactlythe same conditions as those described in connection with preferredembodiment No. 1 above. The results of the measurements taken are shownin Table 2 below. The degree of diametric expansion measured in each ofthe pyrogens following combustion is also indicated in the table.

                  TABLE 2                                                         ______________________________________                                        Preferred              Water temp.                                                                            Absolute Expan-                               embodi-                                                                              Fe.sub.2 O.sub.3                                                                      Fe.sub.3 O.sub.4                                                                      after 5 mins.                                                                          rise in temp.                                                                          sion                                 ment No.                                                                             (%)     (%)     (°C.)                                                                           (°C.)                                                                           (mm)                                 ______________________________________                                        No. 4  70       0      54       34       3-5                                  No. 5  65       5      54       34       2-3                                  No. 6   5      65      44       24       1 max.                               No. 7   0      70      44       24       1 max.                               ______________________________________                                    

Although the expansion of the pyrogens in each of the preferredembodiments No. 6 and No. 7 did not exceed 1.0 mm, a limited amount ofcracking was found to have occurred in each of the pyrogens followingcombustion while some 3.0 g to 4.0 g of the pyrogens remaineduncombusted in both cases.

Preferred Embodiments No. 8 to No. 10

Apart from altering the amount of ferrosilicon (Fe: 25%, Si: 75%) addedto the mixture, the rise in the temperature of the water was in eachcase measured under exactly the same conditions as those described inconnection with preferred embodiment No. 1 above. The results of themeasurements taken are shown in Table 3 below.

                  TABLE 3                                                         ______________________________________                                        Preferred          Water temperature                                                                           Absolute rise in                             embodi- Ferrosilicon                                                                             after 5 minutes                                                                             temperature                                  ment No.                                                                              (%)        (°C.)  (°C.)                                 ______________________________________                                        No. 8   35         48            28                                           No. 9   25         52            32                                            No. 10 20         53            33                                           ______________________________________                                    

In the case of preferred embodiment No. 10, combustion proceededsmoothly although some 0.5 g of the pyrogen was left uncombusted.Following completion of the combustion process, the expansion of thepyrogens was found to measure no more than 1.0 mm in each case.

Preferred Embodiments No. 11 and No. 12

Apart from altering the amount of ferrosilicon added to the mixture, therise in the temperature of the water was in both cases measured underexactly the same conditions as those described in connection withpreferred embodiment No. 1 above. The results of the measurements takenare shown in Table 4 below. Measurements taken on completion of thecombustion process indicated that the pyrogens had in neither caseexpanded by more than 1.0 mm.

                  TABLE 4                                                         ______________________________________                                        Preferred          Water temperature                                                                           Absolute rise in                             embodi- Ferrosilicon                                                                             after 5 minutes                                                                             temperature                                  ment No.                                                                              (%)        (°C.)  (°C.)                                 ______________________________________                                        No. 11  40         42            22                                           No. 12  17         40            20                                           ______________________________________                                    

In the case of preferred embodiment No. 12, some 4.5 g of the pyrogenremained uncombusted.

Preferred Embodiment No. 13

There now follows a description of the preferred embodiment of acanister with a built-in pyrogen as referred to above. FIG. 2 shows anexample of the sort of canister which is designed primarily for use inthe heating of FF. 11 in the figure represents the main body of a steelor aluminum canister, 12 is a pull-top type lid fitted with a ring pull12a and 13 is the base cover of the canister in the middle of whichthere is a hole 13a. The lid 12 of the canister and the base cover 13are each secured to the main body of the canister by means of wraparound jointing. 14 is an inner container the bottom half of which issecured by means of an adhesive in such a way that its wall comes intodirect contact with the inner wall of the main body of the canister 11.Said inner container forms the combustion chamber 14a. 15 is the pyrogenheld in the upper part of said combustion chamber 14a and 16 is aspecial ceramic thermal insulator which supports said pyrogen. More orless in the center of said thermal insulator 16 there is a hole intowhich the ignition device is fitted. The ignition device itselfcomprises an ignition tube 17, which extends through the hole in thethermal insulator 16 almost up to the bottom of the pyrogen 15, anignition agent 18 which is packed into the inside of the ignition tube,an instant high temperature generating ignition material 18a, which islaid on top of the ignition agent 18, thereby constituting the top layerof the ignition device at the point where it meets the under surface ofthe pyrogen 15, and a match head chemical 18b which is fitted in such away that it projects from the bottom end of said ignition tube throughthe hole 13a in the base cover 13 of the canister. 19 is plastic bottomcap, 19a is a plastic top cap and (S) is a thermal insulation sheetwhich may be laid between the thermal insulator and the base cover 13 asand when necessary.

There now follows a description of a typical way in which the FF typecanister of preferred embodiment No. 13 above might be used. First ofall 60 g of pyrogen is inserted into the combustion chamber 14a. 140 gof processed rice (quick boil rice) (R) is then placed in the upperchamber of the canister and a 110 ml pack of water (P) is placed on topof the rice. The lid 12 is then put on to seal the main canister 11. Inorder to cook the rice, first the top cap 19a must be taken off, thenthe pull-top lid 12 must be released by means of the ring-pull fitting.Next the year pack (P) must be taken out of the canister (if theprocessed rice is also enclosed in a pack then this must also, ofcourse, be removed from the canister in the same way) and after openingthe pack, all the water should then be poured over the rice. The top cap19a must then be replaced on top of the canister.

The next step is to remove the bottom cap 19 and rub the chemical strip(not shown in the drawings), which is secured by an adhesive to theunderside of the bottom cap or similar position, across the match headchemical 18b to strike a light. The flame which is generated in this wayis immediately relayed by way of the ignition agent 18 and the instanthigh temperature generating ignition material 18a to the solid pyrogen15 which begins self-combustion in response. The heat generated at thispoint has been measured at 1,400° C.

From the moment that the pyrogen 15 is ignited in the manner outlinedabove, it will then take approximately 10 minutes to produce perfectlycooked and completely scorch free rice. In the case of rice, however, inorder to ensure that it is cooked to perfection, it is always advisableto leave it to steam for a further 5 minutes after the initial cookinghas been completed. In addition, while the rice is cooking, the steamwhich is generated will be discharged from the canister by way of a gapin the top cap 19a while any hot water which might spurt out from theboiling liquid will be trapped by said top cap from where it will rundown through a gap between the main body of the canister and a thermalinsulation sheet (not shown) in the drawings) which is wound around thecanister.

Preferred Embodiment No. 14

FIG. 3 illustrates the preferred embodiment of an FD type canister. Inthe drawing 101 is the main body of a canister formed by the deepdrawing of a sheet metal such as aluminum, for example, and 104 is aninner container formed by pressing the middle part of the base of themain body of the canister 101 inwards in such a way that the wall ofsaid inner container 104 forms a combustion chamber 104a with a fixeddistance between itself and the inner wall of the canister. 102 is thepull-top lid of the canister complete with ring-pull 102a and is securedto the main body of the canister 101 by means of wrap around jointing.103 is the base cover of the canister with a hole 103a at its center. Injust the same way as in preferred embodiment No. 13 described above, theaforementioned combustion chamber 104a contains a pyrogen 105 along witha thick cylindrical thermal insulator 106 made of a special ceramicmaterial with an ignition device located more or less at its center.Said ignition device comprises an ignition tube 107, which extends upthrough the hole in the thermal insulator 106, an ignition agent 108which is packed into the inside of the ignition tube, an instant hightemperature generating ignition material 108a, which rests on top of theignition agent 108 and constitutes the top layer of the ignition device,and a match head chemical 108b which is fitted in such a way that itprojects from the bottom end of said ignition tube 107 through the hole103a in the base cover 103 of the canister. The ring shaped protuberance106a on the upper surface of the aforementioned thermal insulator 106constitutes an inseparable part of the insulator 106 itself.

The aforementioned pyrogen 105 is formed by the compression into a solidflat shape of ferrosilicon powder and a suitable mixture of ferric oxidepowder and a powdered iron oxide of a lower order. The special ceramicwhich is used for the aforementioned thermal insulator 106 consistseither of a substance composed mainly of silicon and baked to give it asponge-like form or else of a suitable mixture of pearlite and clay.Furthermore, both the ignition agent 108 and the instant hightemperature generating ignition material 108a of the aforementionedignition device are each compounds formed by the mixing of fineparticulates of metals and metal oxides. Ideally, the constituents ofthe ignition agent 108 should be capable of being easily ignited by amatch head chemical and also of burning fast. In the case of the toplayer of instant high temperature generating ignition material 108a, onthe other hand, the constituents should ideally be capable of supportinga combustion temperature in the region of 1,000° C. to 1,500° C. 109 isa plastic bottom cap and (S) is a thermal insulation sheet which can belaid between the thermal insulator and the base cover 103 as and whennecessary.

There now follows a description of a typical way in which the FD typecanister of preferred embodiment No. 14 above might be used. First ofall 20 g of the pyrogen 105 is inserted into the combustion chamber104a. 200 ml of coffee liquid (D) is then placed in the upper chamber ofthe canister 101 and the can sealed. When the time comes to heat up thecoffee, first the bottom cap is removed and the chemical strip on theside of the cap used to ignite the match head chemical. The bottom capis then replaced and within approximately one and a half minutes thecoffee liquid inside the canister is heated up to a temperature of about40° C. above the ambient temperature. The coffee is now ready to drink.

Having described the invention in detail and by reference to preferredembodiments thereof, it will be apparent that modifications andvariations are possible without departing from the scope of theinvention defined in the appended claims.

What is claimed is:
 1. A canister for heating food or drink comprising asidewall member, an upper chamber for receiving food or drink, acombustion chamber, and a base having an opening therein, said upperchamber being located within the sidewall of said canister above saidcombustion chamber and being separated from said combustion chamber byan interior wall, said combustion chamber containing a pyrogen and aceramic thermal insulator, said pyrogen being supported on said ceramicthermal insulator, said ceramic thermal insulator having a boretherethrough from the top to the base of said insulator, an ignitiondevice for said pyrogen packed in said bore and extending from the baseof said ceramic thermal insulator to the top of said ceramic thermalinsulator, said ignition device including an instantaneous hightemperature generating material, an ignition material underlying saidinstantaneous high temperature generating material and in contacttherewith and a match head chemical underlying said ignition material atthe base of said bore and extending through said opening in said base ofsaid canister, said pyrogen being a compressed mixture of a ferrosiliconpowder, a ferric oxide powder, and a powdered lower order iron oxide ofthe formula Fe₂ O₃ -x where x is 0.2 to 1.0, said pyrogen having anignition point temperature in the range of about 1000° C. to about 1500°C.
 2. The canister according to claim 1 in which the lower portion ofsaid interior wall of said combustion chamber comes into contact withthe inside side wall of said canister.
 3. The canister according toclaim 2 in which said interior wall is secured to said side wall of saidcanister by an adhesive agent.
 4. The canister according to claim 2 inwhich a food is held in said upper chamber.
 5. The canister according toclaim 4 in which a pack containing water is held in said upper chamber.6. The canister according to claim 1 in which there is a space betweensaid interior wall of said combustion chamber and said side wall of saidcanister.
 7. The canister according to claim 6 in which a drink is heldin said upper chamber.
 8. The canister according to claim 1 in which alid and a base cover are both secured to said side wall of said canisterby wrap around jointing.
 9. The canister according to claim 1 in which aring shaped protuberance is formed on the upper surface of said ceramicthermal insulator.
 10. The canister according to claim 1 in which abottom cap is fitted to the underside of said side wall of saidcanister, said bottom cap carrying a chemical strip which can be used tostrike said match head material.